One Step Formation of Reduced-Graphene-Oxide/CoTMPyP based Electrodes for Oxygen Reduction Reaction

Effective Oxygen Reduction Reaction (ORR) is essential for the development of clean energy fuel cells. The existing Pt-based catalysts are highly efficient but too expensive and rare for mass production. Therefore, low cost non-precious metals catalysts are necessary.

The ORR catalysis using carbon-supported transition metal porphyrins is well known for decades, yet their low activity and stability towards ORR are not sufficient for usage in fuel cells. Recently, graphene and its derivatives, and especially heteroatom doped graphene, have shown promising catalytic ORR activity. The incorporation of Cobalt-porphyrin into a graphene functionalized electrode could supposedly combine the advantages of both catalysts.

In this work we present a simple one step strategy to prepare graphene/Co-porphyrin catalyst on electrode surface instead of the tedious layer-by-layer methods reported so far. Our method is based on the direct electrochemical reduction on glassy carbon of graphene-oxide (GO) in the presence of CoTMPyP (Cobalt-5,10,15,20-tetrakis(1-methyl-4-pyridinio)porphyrin) in the solution. While electrostatic interaction and p-p stacking adsorb the CoTMPyP to the GO in the solution, the electrodeposition of the GO encage the CoTMPyP on the electrode surface.

The ORR activity of glassy carbon electrode that was functionalized using this method was characterized by an onset potential of -0.05V and +0.37V vs. Ag/AgCl in 0.1M NaOH and in 0.1M H₂SO₄ respectively, while reduced-GO functionalized electrode, without CoTMpyP, was characterized by an onset potential of -0.16V and -0.20V vs. Ag/AgCl in the same solutions. Surprisingly, the usage of N-doped-GO have not yielded better results with onset potentials of only -0.13V and +0.15V vs. Ag/AgCl in the alkaline and acidic solutions respectively.